The present invention relates to a power generation system for supplying electrical power to a power distribution system, and in particular (although not exclusively) to a power generation system utilising an alternative energy source such as wind power, wave power and tidal flow.
Alternative energy sources are characterised by the fluctuating nature of the energy source. For this reason, power generation systems using alternative energy sources have typically used a variable speed electrical generator coupled to the energy source, together with power electronics at the output of the generator in order to convert the output of the generator into a form suitable for supply to an electrical grid.
With the development of variable speed drive technology, it has now become feasible to use synchronous generators running at synchronous speed in alternative energy power generation systems. Synchronous generators have the advantage that they can be directly connected to the grid, and that their behaviour when connected to the grid is predictable.
Alternative energy sources are often located at long distances from centres of population, and may require long transmission lines to supply power to areas where it is needed. Long transmission lines tend to create a capacitance effect due to the long parallel conductors. This in turn may cause the system to have a leading power factor. If the leading power factor becomes too pronounced the system may become unstable.
Under normal conditions a leading power factor may be compensated by reactive loads in the system, or by the grid company switching in reactors at power sub-stations. However during periods of light loads the leading power factor may not be adequately compensated in this way. One solution in such situations would be to disconnect some transmission lines. However this may result in inefficient use of the energy which is potentially available from alternative energy sources.